The preparation of chemically-reactive, quinonoid derivatives of several known inhibitors of cyclooxygenase is planned. Specifically, derivatives of salicylic acid, flufenamic acid, indomethacin, and phenylbutazone will be prepared. The elucidation of specific molecular mechanisms for inhibition of arthritic inflammation is a goal of this research (based on the recognized significance of prostaglandin biosynthesis in the inflammatory process). Recent techniques for purification of cyclooxygenase, a component of the prostaglandin synthetase system, will allow the direct determination of active-site residues involved in mechanisms of inhibition by these non-steroidal anti-inflammatory (NSAI) agents. Design of these affinity labels is based upon the known metabolic routes of the NSAI agents, and the presumed capability of the agents to undergo one-electron oxidation in vivo possibly leading to electrophilic, free-radical species at the active-site of cyclooxygenase. The proposed labelling agents maintain the electrophilic reactivity of the hypothesized free-radicals and they maintain the significant structural parameters of the known NSAI agents (Cyclooxygenase inhibitors). Synthesis of these new, site-directed inhibitors of cyclooxygenase will provide the means for elucidation of mechanisms of this inhibition, and may provide more potent, specific inhibitors of prostaglandin synthesis for therapeutic use in arthritis. The initial emphasis of this investigation must be the chemical synthesis of the oxidized NSAI derivatives. In most cases the development of efficient synthetic methods for these new compounds will involve the experimental determination of optimum techniques for production, isolation, and purification of such chemically-reactive species. Concurrent with the synthetic process the isolation of cyclooxygenase, or the arrangement of access to purified enzyme through collaboration, will proceed. The immediate determination of chemical reactivity of these agents as they become available can proceed with model nucleophiles. Determination of functional groups of cyclooxygenase which covalently interact with the designed labelling agents would be determined by normal protein degradative techniques utilizing radio-labelled agents.